During the past month, ENSO-neutral continued, with near-average sea surface temperatures (SSTs) established across most of the equatorial Pacific Ocean [Fig. 1]. With the exception of the easternmost Niño-1+2 index (+0.8°C), the latest weekly Niño SST index values ranged from -0.3°C to +0.0°C [Fig. 2]. Subsurface temperature anomalies in the eastern Pacific Ocean became weakly negative over the past month [Fig. 3], with below-average temperatures generally observed between 25- and 200-meters [Fig. 4]. Low-level wind anomalies were easterly over the east-central and eastern tropical Pacific, while upper-level wind anomalies were westerly over the west-central and eastern tropical Pacific. Convection remained enhanced over a small region of Indonesia and was suppressed over the western tropical Pacific [Fig. 5]. Collectively, the coupled ocean-atmosphere system in the tropical Pacific reflected ENSO-neutral.

The IRI predictions indicate ENSO-neutral is most likely to persist through the Northern Hemisphere winter 2025-26 [Fig. 6]. However, similar to last month, the North American Multi-Model Ensemble favors La Niña conditions for a short duration during the Northern Hemisphere fall and early winter. Based on this guidance and recent changes in the tropical Pacific, the forecast team narrowly favors La Niña thresholds being reached in three overlapping, 3-month seasons (Niño-3.4 index ≤ -0.5°C during September-November, October-December, and November-January). In summary, ENSO-neutral is most likely through the late Northern Hemisphere summer 2025 (56% chance in August-October). Thereafter, a brief period of La Niña conditions is favored in the fall and early winter 2025-26 before reverting to ENSO-neutral [Fig. 7].